As an example of a hinge mechanism HM, there is taught in Japanese Patent Application (Laid-Open) No. 8-116185 a torque hinge device which includes a bearing portion provided to a casing of a liquid crystal portion, a shaft portion provided to a casing of a main body portion and rotatably inserted into the bearing portion in a state where a frictional resistance is generated, and a ring-shaped elastic member fixedly fitted to a groove portion provided along a circumferential direction of the bearing portion. An unevenness is formed on an inside surface of the bearing portion and an outside surface of the elastic member so that the surfaces interlock with each other.
In the torque hinge device, when the casing of the liquid crystal portion is opened and closed, since the unevenness having a smooth curved shape is formed on the inside surface of the bearing portion and the outside surface of the elastic member to interlock with each other, the elastic member rotates with a convex portion on the outside surface thereof being repeatedly extended or contracted by a convex portion on the inside surface of the bearing portion. Therefore, it is possible to perceive a sense of lock-feeling at a position where the unevenness of the inside surface of the bearing portion and the outside surface of the elastic member interlock with each other. Moreover, since the frictional resistance is always generated between the inside surface of the bearing portion and the outside surface of the elastic member when the casing of the liquid crystal portion is rotated, it is possible to obtain an opening/closing torque.
As another example of a hinge mechanism HM, there is taught in Japanese Patent Application (Laid-Open) No. 2001-065543 an opening/closing torque variable tilt hinge which includes a bearing cylinder provided to a cover and having an end portion thereof fixed to an attachment arm, a shaft provided to a device body and rotatably inserted into the bearing cylinder, four coil springs mounted on an outer circumference of the shaft and having an outwardly bent projection at one end thereof. The bearing cylinder has formed therein a slit in which the projection is fixed in an opposing and closely contacting state so that a winding direction of a set of coil springs is reversed and a notch which engages with the projection in an opposing and closely contacting state while allowing the projection to rotate by a predetermined angle so that the other set of the coil springs is reversed.
In the opening/closing torque variable tilt hinge, since the bearing cylinder is rotated through the intervention of the attachment arm in response to an opening/closing of the cover, the respective coil springs fasten the shaft by the rotation of the bearing cylinder, and thus an opening/closing torque is generated by a frictional resistance. Since the attachment directions of the pair of coil springs are different, either an opening torque or a closing torque is always generated by the coil springs when the cover is opened or closed. Moreover, when the cover is opened by a predetermined angle, the cover can be easily lifted up by the opening/closing torque of a set of coil springs. When the cover is lifted up by more than the predetermined angle, the opening/closing torque of the other set of coil springs is increased. Therefore, it is possible to vary the opening/closing torque when the cover is opened and closed.
As a further example of a hinge mechanism HM, there is taught in Japanese Patent Application (Laid-Open) No. 2006-112523 a hinge mechanism which includes a shaft member in which magnetic poles are arranged in the order of N, S and N in the circumferential direction of an outer circumference thereof and a rotary member in which magnetic poles are arrange in the order of S, N and S in the circumferential direction of an inner circumference thereof, and in which the magnetic pole portion of the shaft member is inserted. The hinge mechanism is capable of determining the position of the rotary member at an arbitrary position during the rotation without using any mechanical mechanism.
In recent years, a display unit incorporated into a cover of the notebook PC has become larger in its size. Since a weight of the cover increases when the size of the display unit increases, the cover is likely to fall down. The opening/closing torque needs to be set high.
However, in the torque hinge device of Japanese Patent Application (Laid-Open) No. 8-116185 and the tilt hinge of Japanese Patent Application (Laid-Open No. 2001-065543), since the opening/closing torque is generated by the frictional resistance, when the opening/closing torque is set high, there may occur an occasion in which the main body is lifted up together with the cover by an operating force for opening the cover. Therefore, there was a drawback that it is difficult to lift up the cover with one hand.
In the hinge mechanism of Japanese Patent Application (Laid-Open No. 2006-112523), since the position of the cover is determined by not the frictional resistance but an attractive force of opposing permanent magnets, it may be possible to lift up the cover with one hand even when the size of the display unit is increased. However, it was difficult for the permanent magnet to control the opening/closing torque.
Thus, a need has been recognized for a hinging device that addresses the shortcomings of conventional hinge devices, as outlined above.